The following background information may present examples of specific aspects of the prior art (e.g., without limitation, approaches, facts, or common wisdom) that, while expected to be helpful to further educate the reader as to additional aspects of the prior art, is not to be construed as limiting the present invention, or any embodiments thereof, to anything stated or implied therein or inferred thereupon.
Often, log yard wastes are typically bark and woodchips mixed with soil, oversized logs and undersized limbs, metal-containing logs, and mold damaged chips. Typically, log yard waste for sawmills forms the largest solid waste stream. Sawmills with on-site landfills will often use some of this material as landfill cover, but there is often more waste than needed for this purpose.
It is known that a continuing problem in log yards is the accumulation of log debris. The log debris often becomes mingled with rock and soil, forming an aggregate. Attempts to stabilize the wet aggregate to improve traction for equipment results in additional gravel and rock being added. Decomposition of the wood portion of the aggregate results in the production of noxious by-products that are more frequently being viewed as environmentally unacceptable. The aggregate is essentially a combination of three particulate components, namely high density mineral particles, low density wood particles, and relatively fine soil particles.
Log yard operators have, to date, sought methods to treat the mixtures, with unsatisfactory results. Often, attempts are made to separate mixtures of wood pieces, rock, and soil particles so that the components of the mixture can be reused. In one commonly used process, disk screens are used for separating the mixture into small particles, which are a mixture of soil particles and small wood particles, large wood chunks, and a mixture of gravel size rock and wood pieces of about the same size. Additional attempts have been made to separate the rock from the wood pieces by air streams and the force of gravity, with varying degrees of success.
Those skilled in the art are familiar that other log yard waste separation techniques tried have included flotation for separating the wood from the mineral portion, expecting the wood to readily float free. This approach has been unsuccessful due to the large fraction of wood that is waterlogged and will not float. Additionally, the water used for flotation becomes contaminated and becomes a further liability.
It is known that sawmill logs are increasingly being stored on land rather than in log ponds so as to reduce water pollution. Usually these log storage yards are bedded with gravel. As the logs are moved into and out of the storage yard, chunks of bark and other wood debris fall from the logs and mix with the gravel. This yard bark is removed periodically from the yard to keep the yard clean and reduce the fire hazard. One common method of removal is to scoop up the gravel-bark mixture with a front end loader-type vehicle and dump it someplace as waste. This results, however, in the removed gravel and bark being a complete loss. And thus, the gravel must be replaced with new gravel at considerable expense. Additional expense is involved in transporting the bark-gravel mix to a dumping site.
It is also known that air separation or elutriation techniques have also been attempted in the past. The difficulty with typical elutriation techniques is that they are as likely to lift and separate out small particles of high density rock as they are to separate out larger pieces of low density wood. The product still remains a mixture of mineral and wood particles.
Other proposals have involved mechanically separating the larger and smaller materials of log yard waste. The problem with these separation methods is that they are not powered through hydraulic power, so as to reduce power consumption and reduce fire hazards. Also, the prior art does not strategically position dampening fingers, accelerator plates, and dampening plates across multiple conveyors to regulate the speed of the materials. Even though the above cited log yard waste separating systems and methods meets some of the needs of the market, a hydraulic separation system that enables efficient recycling of log yard waste from an elevated frame into fine granules, small rocks, small bark, large bark, and large rocks with a variety of sequentially positioned, hydraulically powered separating components is still desired.